Continuous Global Positioning System (CGPS) Stations

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Measurements of elevations, aquifer-system compaction, and water levels are used to improve our understanding of the processes responsible for land-surface elevation changes. Elevation or elevation-change measurements are fundamental to monitoring land subsidence, and have been measured by using continuous GPS (CGPS) measurements and campaign global positioning system (GPS) surveying.

Continuous Global Positioning System (CGPS) Station P303 in Los Banos, CA.A CGPS station continuously measures the three-dimensional (3D) position of a point on, or more specifically, near the earth's surface. For this study, scientists are primarily interested in vertical movement (subsidence and uplift), but horizontal movement can be obtained with CGPS and can also be informative for subsidence studies. CGPS stations are used to monitor subisdence in California's Central Valley. (Credit: Michelle Sneed, USGS. Public domain.)

These GPS stations generally collect position information every 15 seconds which are then processed to produce a daily position. These daily positions are then concatenated to produce a daily time series, which allow us to track the 3D position of the station.

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The CGPS data were obtained from the UNAVCO Plate Boundary Observatory (PBO) network of continuously operating GPS stations. The PBO is the geodetic component of UNAVCO, a consortium of research institutions whose focus is measuring vertical and horizontal plate boundary deformation across the North American and Pacific Plates in the western U.S. using high-precision measurement techniques....

During the recent droughts of 2007-2010 and 2012-2017, groundwater pumping has increased from the combined effects of the drought and land-use changes, re-initiating land subsidence. In order to document historical subsidence and monitor continued changes, the USGS has gathered and interpreted data from a variety of sources.